1. Field of the Invention
The present invention relates to a circuit for switching a single phase AC operated device between the on and off states and, more particularly, to a switch for controlling an AC motor in a refrigerator control circuit.
2. Description of the Prior Art
Several control circuits are known for controlling AC operated devices in response to temperature changes in an environment. For instance, Jones U.S. Pat. No. 3,829,010 discloses a thermostat for power ventilators and the like. A power ventilator fan is driven by an electric motor connected in series with a triac, the triac being triggered in response to temperature changes detected by a pair of thermistors. Triggering of the triac closes a circuit to the motor to cause the operation thereof.
An on-off control means for an inductance means, such as a single phase AC motor, is disclosed in Schmidgall U.S. Pat. No. 3,707,776 which operates by resonance to selectively cause voltage and current to be out of phase with each other and thereby prevent operation of the inductance drive means. The disclosed circuit includes two capacitors C1 and C2, C2 being connected across a circuit including a motor in series connection with a parallel combination of an SCR and a reverse-poled diode. The capacitor C1 is connected in series with the rest of the circuit as a whole. When the SCR is not being gated, the capacitors C1 and C2 charge at each half cycle of the alternating current supply and then discharge and recharge with an opposite polarity on each subsequent half cycle. The current through the capacitors C1 and C2 will be out of phase with the current through the inductive motor device, causing the voltage across the motor to be zero. Current flows through the capacitors C1, C2 and the motor, even while the motor is deenergized.
Refrigerator and freezer control circuits are often found within the refrigerated compartments of the respective refrigerator or freezer and, therefore, any heat generated by the control circuits is transmitted to the refrigerated compartment. Thereafter, the heat must be removed from the compartment by the cooling apparatus. The generation and subsequent removal of heat from the refrigerated compartment results in multiplying the energy penalty of using an inefficient control circuit. Thus, to avoid this wasteful practice, control circuits, particularly those for use in refrigerated compartments, should be as energy efficient as possible.